Steam generation and compositions for inhibiting foam therein



STEAM GENERATION AND COMPDSITIGNS FOR ITING FUAM THEREIN 12 Claims. or. 252-321 The present invention relates to improved antifoaming compositions which are added to water'that -is subjected to boiling, as in the boilers of locomotives, stationary steam generators, ev'aporators, ,and in other instances where the boiling of water occurs, especially under superatmospheric temperature and pressure conditions, whereby the tendency of the water therein to foam is prevented or reduced and the boiling characteristics of the'water carryover of boiler water with the steam therefrom is prevented. I

It is well known that in the operation of steam boilers, such as in railroad locomotives, in electric power plants and the like, or in other boiling operations where steam is formed, as for example in evaporators, that the water therein, even though initially it shows little tendency to foam, will, when the amount of total dissolved solids approaches a relatively high concentration due to the production of steam, develop avery decided tendency'to foam. This foaming of the water'in a boiler producing steam is characterized not only by an ac'cumulationof relatively stable froth or foamwon the surface of the boiler water but also by the formation at the heat transfor surfaces in the boiler of extremely small steam bubbles. These minute bubbles show almost no tendency to coalesce and the result is that the'entire volume'of 7 water in the steam generator is lifted in the form :of so called light water, which is actually an intimate mixture of boiler water and tiny steambubbles. When this occurs, considerable quantities of boiler water are physically carried out of the .boilers or evaporators with the steam, thereby introducing solid matter into the steam lines and into the eventual condensate.

Such carryover has-many disadvantages/because it tends to contaminate and restrict the steam lines, to plug or corrode the valves,

,' to deposit on turbine blades, to plug and cause burning out of superheater tubes, and under serious conditions may even impair the cylinders and piston rods of steam engines or otherwise render the steam unfit for use.

The carryover is frequently due in part, at least, to priming, or what may be described as surging or boiling over of the water.

Attempts havebeen made in thepast to'control' foaming and priming by controlling the dissolved solids'content of the water as by excessive blow-down of the In the first place, these fatty materials or glycerides are very unstable under severe hydrolytic conditions encountered in steam genera- I tiom-particularlyunder the conditions of superatmostes atent so improved that priming. of the steam generator and ICC . 2 Y I I pheric pressure, the corresponding high temperatures and the alkalinity of theboiler water.

to accumulate in such a way as to' give a compound dirty boiler, necessitating frequent washing. Furthermore, in many instances certain o'f the decomposition products thus produced, or sometimescven thematerials themselves, have a definite volatility iwith steam and will, A therefore, steam-distill ont of the steam generators, thus} appearing in the steam and in the eventual 'condensate.

This, of course, is alsoundesirable. Additionally, such types of antifoaming agents usuallyare. of such {a low order of efliciency that they haveto' be employed inrelatively large quantities, adding not only to the expense but also to the inconvenience of operatingcthe, steam.

generators; and since they are so unstable their effective:

ness is of short duration, necessitating the continual charging into the boilers or other steam generators. of

many of the disadvantages of the former, especially in I that they were highly eilicient at lower dosagelevels and much more resistant to decomposition, so that their efiective life was relatively greater. I

One of the objects of this inventionis to provide a s new and improved process for preventing the foaming other hand, quite dt'eficientin that they introduce new i difiiculties which, in some-instances, are worse than the conditions they'are intended to cure.

and priming of steam generators, thus improving the quality of the steam produced thereby.

Another object is to provide new and improved ,co'm-- positions for adding to the water in a steam generator to prevent or reduce its tendency to foam.

Another object is to provide antifoaming compositions which are effective to prevent foaming when used in very low dosages.

A further object is to provide highly elfective antifd'arri' compositions which are readilyand easily dispersible when added to the feed water entering a steam generator.

Another object of this invention is to provide antifoam compositions in which the active efiective ingredients are readily soluble in water at relatively low ternperatlllres (e. g., ,7 5 F.) but decrease in solubility when the water is heated to relatively high temperatures such as are employed in the generation of steammndersuperatmos pheric pressures and the corresponding temperatures.

Still another object of the invention is topro'videa process of generating steam and new and improved antifoam compositions therefor wherein the period 0f effec; tiveness of the antifoam composition is greatly priolonged as compared to the period of effectiveness of other. antifoam compositions presently known in the art.

Still another object 10f the invention is to providea new and improved process of inhibiting foaming during steam generation. which permits operations ,at'l higher dissolved solids contents than has heretofore been. considered possible.

An additional object is to. provide new and useful antifoaming compositions of an extremely highQorder. of resistance to decomposition under the conditions pr evail Other objects. will. appear here-,

ing in steam generation. inafter.

In accordance with this invention, it has nowbeen discovered that there is a series of compounds that are designated as high molecular weight 'polyoxyalkylene diols, characterized by the presence in the pblyoxy r r 2,846,404 Patented Aug. 5, 8v

The resultant ae- 1 A composition products which remainin the boiler tend to l increase the foaming tendencies of the boiler water and alkylene chain of one or more oxymethylene groups. These diols possess several important advantages over formerly known antifoam compositions. They are all much more effective than any of the fatty glycerides, and many are more effective than any hitherto known materials. Furthermore, they are much more stable to decomposition under conditions of use than any of the glycerides or polyamides, thus giving them a greatly prolonged period of effectiveness in preventing foaming. In general, they are more readily dispersed in the water being fed to the steam generator than are older materials, and a further advantage offered by many of these diols is that they are liquids or very low-melting waxy materials which are readily soluble at ordinary temperatures.

The diols preferably employed in the practice of this invention may be represented by the structural formula wherein n is an integer equal to 2 or more, and may have severalvalues in the same compound, and x and y are integers of one or more. Such' compounds are thus seen to include polyoxyalkylene diols, in the polyoxyalkylene chain of which appears at least one oxymethylene group, and in which there are also other (larger) oxy'alkylene groups. By these larger oxyalkylene groups is meant oxyalkylene groups which are not oxymethylene or' substituted oxymethylene groups. Examples of these large oxyalkylene groups are Oxyethylene (OCH CH Oxypropylene o oH2cH and -o CHQCHfCHQ) a Oxybutylene -6 03114011 o onzonon -ooH','o'HroH2on El; lHa

- CH+CH- and -oo Ht'oH and oxyalkylenes of greater number of carbons such as oxyp'ent'arn'ethylerie, oxyhexamethylene, oxydecamethylene and higher homologues. The larger oxyalkylene groups present in the polyoxyalkylene chain may all be the same, or theyt'nay be different,- so that several are present in the same chain. When the larger oxyalkylene groups are not all the same, they may occur in the chain in various proportions and in a random or irregular sequence, with respect to each other.

In order that these diols possess the property of efficiently preventing the foaming and priming of steam generators, they should be of relatively high molecular weight, i. 6., either x or y, or both, in the formula should be. of such size that the total molecular weight of the diol will be greater than a certain value. Since, as will be seen by the discussion to follow hereinafter, the usual synthetic methods for the production of the diols of this invention leads to a mixture of products very closely similar in chemical structure but of differing molecular size, it is only possible, in speaking of the molecular weight of these compounds, to refer to an average value of molecular weight for the mixture of polymers.

The products employed in accordance with the invention may also be described as addition products of formaldehyde with aliphatic dihydric alcohols.- It is essential for the purpose of the invention that the" addition products be substantially insoluble in the boiler water under the conditions of steam generation. Many of these addition products have the advantage that they are substantially soluble in water at room temperatures of say F. or even at somewhat higher temperatures used in preheaters, and hence can be readily dispersed in the boiler feedwater. They are further characterized, however, by the fact that they decrease in solubility upon heating to steam generating temperatures. The molecular weight of the addition product and the kind and type of oxyalkylenc groups therein are all factors contributing to its water insolubility at the elevated temperatures used in steam generation. In view of the characteristic of decreasing solubility of these addition products with increasing temperatures, the temperature at which the steam is generated is also a factor. Thus, compounds which do not have the desired antifoam efficiency in boilers operating at 250 pounds per square inch may have such efficiency in boilers operating at 1000 to 1500 pounds per square inch. Routine tests can be used to determine Whether a given addition product has the requisite insolubility under the steam generating conditions to be used.

It will be noted in the foregoing formula that n must have a value of at least 2. In other words, the aliphatic dihydric alcohol from wihch the addition products are prepared must have their hydroxy groups spaced by at least four carbon atoms. Vicinal glycols, which have hydroxy groups too close to each other, tend to form ring compounds such as dioxolane or dioxolane derivatives and are unsuitable for the purpose of the invention.

The oxymethylene group in the addition product is supplied by the formaldehyde reactant.

The addition products are prepared with formaldehyde because it forms compounds of high molecular weight when reacted with low molecular weight aliphatic dihydric alcohols. Other aldehydes and ketones do not react so readily and usually form only a dimer of the aliphatic dihydric'alcohol. The preferred reactants used to form the addition products are formaldehyde and polyoxyalkylene glycols containing two to five carbon atoms in their oxyalkylene groups. The oxyethylene group is relatively hydrophilic and hence where the polyoxyalkylene glycol reacted with the formaldehyde contains all oxyethylene groups relatively high molecular weights must be attained in order to secure the desired insolubility in the hot boiler water. Higher oxyalkylene groups such as those derived from 1,2-propylene oxide are more hydrophobic and where these groups are present as the sole oxyalkylene groups in the polyoxyalkylene glycol, the addition product can have a much lower molecular weight.

The reaction between the formaldehyde and the aliphatic dihydric alcohol is carried out in the presence of a suitable catalyst either under dehydrating conditions or, alternatively, the aliphatic dihydric alcohol can first be reacted with the formaldehyde and then the water formed in the reaction can be removed from the reaction zone.

The reaction between the glycol and the formaldehyde is preferably carried out at moderate temperatures, for example, between 50 C. and C., with or without a solvent as a diluent. To accelerate the reaction Friedel- Crafts catalysts are preferably employed, for example, aluminum chloride, ferric chloride, titanium tetrachloride, stannic chloride, borontrifluoride, and acid compounds such as sulfuric acid, benzene sulfonic acid or acid cation exchangers containing strongly acidic groups such as the sulfonated' polymer of styrene and divinylbenzene, sulfonated phenolformaldehyde resin, sulfonated coal or the like.

The reaction is preferably carried out under very strong dehydrating conditions facilitating the removal of water from the reaction mixture. In the practice of the invention' two different methods have been employed effectively.

' In one case aromatic hydrocarbons, such as benzene,

. slow stream of dry air to give the strong dehydrating conditions necessary. Other methods of preparation in which very strong dehydration conditions exist are also suitable for the preparation of the compounds of this invention.

In order to separate and collect the water formed in the reaction it is convenient to carry out the reaction in benzene solution. The benzene is distilled slowly and the water distilling with the benzene is separated. The benzene is then returned to the reaction zone. The water collected is measured and the progress of the reaction can be followed in this way. A convenient apparatus for carrying out this reaction consists of a Dean-Stark moisture trap fitted with a reflux condenser and a round bottom boiling flask. A time full of a desiccant, such as calcium chloride, is preferably attached to the open end of the reflux condenser to prevent the condensation of the moisture from the atmosphere.

The formaldehyde used in the reaction can be added as an aqueous solution called formalin, or as solid trioxane (alpha-trioxymethylene). The solid alpha-trioxymethylene is preferred since the amount of Water formed in the reaction is preferably used as a guide in following the extent of the reaction. It is well known that trioxane (alpha-trioxymethylene) decomposes to liberate monomeric formaldehyde when heated in the presence of acidic materials such as zinc chloride, ferric chloride, etc.

The products employed for the purpose of the invention haverelatively high molecular weights, preferably at least 1000 and in some cases as high as 11,500, or higher.

In order to evaluate the effectiveness of these addition products tests were made on an experimental boiler of the type described in the publication Solid matter in boiler water foaming by Foulk and Brill, which appeared in the periodical Industrial and Engineering Chemistry, vol. 27, pages 1430-35. This boiler was fitted with sight glasses on each side of the steam release space so that conditions in the boiler in a zone several inches above and below the normal water level were observed while the boiler was operating under pressure. It was also equipped with an automatic water level control which held the water level within a range of 10.25 inch.

In the series of experiments described below, a feedwater (herein referred to as a 70 grain water) was used having the following composition, expressed in parts per million, by weight:

Calcium hardness (as CaCO 154.0 V Magnesium hardness (as CaCO 154.0 Alkalinity (methyl orange) (as CaCO 726.0 Sodium chloride (as NaCl) 85.5 Sodium sulfate (as Na SO 718.0 Tannin extract, dry"; 34.2

To this feedwater was added the antifoam composition of the character and in the quantity specified in the specific experiment, and this water-was then gradually concentrated in the test boiler by evaporation at the rate of six gallons per hour at 250 pounds per square inch (p. s. i.) gauge pressure. A continual recording was made of the relative conductivity of the condensate from the boiler, and continual observations were made of the character of the boiling and the amount of foaming as seen through the'sight glasses. When the antifoam thus introduced continuously with the feedwater was no longer able to overcome the foaming tendencies brought about by the concentration of dissolved solids in, the boiler water, the

foam height became great enough to cause boiler water to be carried out of the boiler with the steam, and this end-point of the test was determined both by observation boiler water was withdrawn from the boiler and analyzed,

At this end-point, a sample of the and the eifectiveness'of the antifoam expressed in terms of the total dissolved solids concentration which it permitted the boiler to carry. A high value of total dissolved solids (T. D. S.) indicates an effective antifoam. With no antifoam, this feedwater gives a carryover at a total dissolved solids value of approximately grains per gallon.

The following examples illustrate some of of these tests.

the results EXAMPLE I The material tested was an addition product of alpha trioxymethylene with Carbowax 1000 and Polyglycol P400 in approximate molar ratios of 2:1:1 and having an intrinsic viscosity in benzene of 0.0915. At a dosage of 0.005 grain per gallon of feedwater the total dissolved solids in the boiler water averaged 733 grains per gallon in two tests before carryover occurred.

EXAMPLE II The material tested was an addition product of alpha trioxymethylene with Carbowax 1000 and Polyglycol P-400 in approximate, molar ratios of 2:1:1 and having an intrinsic viscosity in benezene of 0.0925. At adosage of 0.005 grain per gallon of feedwater the total dissolved solids in the boiler water averaged 633 grains per gallo in two tests before carryover occurred.

EXAMPLE HI The material tested as an antifoam in this example was an addition product of alpha trioxymethylene and Polyglycol P-400 having anintrinsic viscosity in benzene of 0.0380. At a dosage of 0.005 grain per gallon of feedwater the total dissolved solids in the boiler Water aver- H aged 789 grains per gallon in two tests before carryover occurred.

EXAMPLE IV The material tested as an antifoam in this example was an addition product ofalpha trioxymethylene and Polyglycol P-400 made with an additional quantity of trioxymethylene and having an intrinsic viscosity in benzene of 0.0368. At a dosage of 0.005 grain per gallon of feedwater the total dissolved solids in the boiler water' averaged 648 grainsper gallon in two tests before carryover occurred.

EXAMPLE V EXAMPLE VI The material tested as an antifoam in this example was an addition product of alpha trioxymethylene and Polyethylene Glycol 900. When dissolved in the boiler feedwater at a dosage of 0.005 carryover did not occur until the total dissolved solids in the boiler water had reached 3118 grains per gallon.

" EXAMPLE VII The material tested asan antifoam in this example was an addition product of alpha trioxymethylene with Polyethylene Glycol 600 and 1,5-pentane diol in the molar ratio of 0.l:0.05:0.05. Whendissolved in the boiler feedwater at a dosage of 0.01 carryover did not occur until the total dissolved solids in the boiler water had reached 414 grains per gallon. Y

EXAMPLE VIII The material tested as anantifoam in this example was an addition product of alpha trioxymethylene and Carbo wax 1000reacted in a molar ratio of 1:1. When tlis- 7 solved in the boiler feedwater at a dosage of 0.005 ,grain per gallon carryover did not occur until the total dissolved solids in the boiler water hadreached 2947 grains per gallon.

EXAMPLE IX The material tested as an antifoam in this example was alpha trioxymethylene and PolyglycolP-1200 reacted in substantial equimolar proportions. The addition product was made up into a dry-appearing pulverized composition by mixing 3 parts by weight of the addition product with 1 part by weight of oleic acid, 1 part by weight of dipropylene glycol .and grinding the resultant mixture with 95 parts by weight of a dry pulverized lignin derivative commonly used in boiler water treatment and made by desulfonation and partial depolymerization of sodium lignin sulfonate by treatment with aqueous alkali at high temperature. This material exhibits an excellent dispersing effect on the antifoam addition agents but neither it nor the oleic acid nor the dipropylene glycol themselves exert an antifoam effect in the boiler. The dry pulverized antifoam composition was added to the feedwater at a dosage of 0.167 grain per gallon resulting in a concentration of the antifoam addition product in the feedwater of 0.005 grain per gallon. This permitted a total dissolved solids concentration in the boiler of 875 grains per gallon before carryover occurred. 'When the same product was tested at a concentration of 0.0075 grain per gallon in the feedwater a total dissolved solids concentration of 956 grains per gallon was permitted before carryover occurred. At a dosage of 0.010 grain per gallon of the antifoam in the feedwater a total dissolved solids concentration in the boiler Water before carryover occurred was 576 grains per gallon. At a dosage of 0.015 grain per gallon of the antifoam in the feedwater the total dissolved solids concentration in the boiler before carryover occurred averaged 493 grains per gallon.

EXAMPLE X The antifoam material tested in this example was the addition product of alpha trioxymethylene with Polyethylene Glycol 300 and Polyglycol P400 reacted in molar ratios of 0.10:0.052005. This addition product exhibited such a pronounced antifoam efficiency that an accelerated test was used. In order to provide an accelerated test a feedwater (herein referred to as a 210 grain water) having the following composition, expressed in parts per million by weight, was used.

Calcium hardness (as CaCO 178.0 Magnesium hardness (as CaCO 185.0 Alkalinity (methyl orange) (as CaCO 1,370.0 Sodium chloride (as NaCl) 334.0 Tannin extract, dry 51.0 Sodium sulfate (as Na SO 1,950.0

The test procedure was otherwise the same as previously described for 70 grain water except that the carryover point was between 300 and 450.

When so tested at a dosage of 0.005 grain per galllon the previously described addition product permitted a total dissolved solids concentration of 6850 grains per gallon in the boiler water before carryover occurred.

The exact procedures used in preparing these compositions are subject to some variation. The following examples are given to illustrate the specific details of preparation of the compositions described in the previous examples.

EXAMPLE XI The composition of Example I was prepared as follows.

One hundred (100) grams of Carbowax 1000 and 75 grams of Polypropylene Glycol 750 was treated with 3.0 grams of alpha trioxymethylene and 0.5 gram of ferric chloride in 150 ml. of benzene. The mixture was heated gently for live hours, avoiding refluxing during this period. The mixture was then heated more strongly so that the mixture refluxed. The refluxing was continued for several hours, at which time 1.1 ml. of water were removed from the reaction mixture. Another 3.0 grams of alpha trioxymethylene was then added and the above procedure repeated. Another 0.5 gram of alpha trioxymethylene was added and the mixture refluxed for 7 hours. At the end of this time 5.4 ml. of water was found in the trap, making a total of 6.5 ml. of Water removed from the reaction mixture. The theoretical volume of water to be exp cted was 3.6 ml. The excess water must have condensed on the cold finger from the air in the room and run down into the trap.

The reaction mixture was refluxed with 2.0 grams of potassium acetate for several hours, filtered, and the LQlVClli removed under reduced pressure on the steam bath. The viscous dark brown liquid thus obtained solidified to a soft Wax-like consistency on cooling.

Three grams of this solid was ground thoroughly with 97 grams of desulfonated and partially depolymerized sodium lignin sulfonate in a mortar and passed through a mesh screen.

EXAMPLE XII The composition of Example II was prepared as follows.

grams (0.1 mol) of Polyethylene Glycol 1000, 75 grams (0.1 mol) of Polypropylene Glycol 750, 5.4 grams (0.18 mol) of alpha trioxyrnethylene, 0.5 gram of ferric chloride and grams of benzene are heated just. below reflux point for one day (7 hours). The mixture was then refluxed until /2 of the theoretical amount of water was removed. 0.5 gram of alpha trioxymethylene was added, heated mildly for some hours and then additional amount of water was removed. Three more 0.5 gram portions were added as above until the theoretical amount of water was removed (3.6 cc.). 1 gram of potassium acetate was then added and the mixture refluxed for one hour. The solution was filtered while hot and the benzene removed with vacuum on a steam cone. The product was a soft brown waxy solid, which melted somewhat at higher than room temperature.

EXAMPLE XIII The composition of Example III was prepared as follows:

EXAMPLE XIV The composition of Example IV was prepared as described in Example XIII except that eight additional 0.5 gram portions of alpha trioxyrnethylene were added and 96% of the water theoretically formed was removed. This product was also a viscous liquid.

EXAMPLE XV The product of Example V was prepared as described in Example XIII except that 0.5 gram of aluminum chloride was used in place of the stannic chloride and there were six 0.5 gram additions of alpha trioxymethylene. The amount of water removed was 86% of that theoretically formed. This product was also a viscous liquid.

EXAMPLE XVI The composition tested as described in Example VI was prepared from the following ingredients:

40 grams of Polyethylene Glycol 900 (0.044 mol) ferric chloride were mixed with the benzene.

2 grams of alpha trioxymethylene (0.067 mol), 0.2 gram of ferric chloride 70 ml. of benzene.

EXAMPLE XVII The'composition tested as described in Example VII Was prepared from the following components:

' 30 grams Polyethylene Glycol 600 0.05 mol) 5.2 grams l,5-pentanediol (0.05 mol) 3.0 grams alpha trioxymethylene (0.10 mol) 0.2 gram ferric chloride 70.0 ml. benzene The glycol, pentanediol, alpha trioxymethylene and ferric chloride were mixed in the benzene and the henzene was distilled, the water separated,-and the benzene returned to the reaction zone until 1.8 ml. of water was [collected The ferric chloride was neutralized with potassium acetate and benzene 'was removed under vacuum. The product was a viscous liquid.

N, H 'EXAMPLEXVH I: V

The composition tested as described in Example VIII was prepared from the following components:

50 grams of Carbowax 1000 (0.05 mol) 1.5 grams of alpha tr-ioxymethylene (0.05 mol) 0.2 gram of ferric chloride The Carbowax, alpha trioxyrnethylene and ferric chloride were mixed and heated at 80 C. under vacuum with .was prepared from thefollowing components; '40 'grams'of Polyglycol P-1200 (0.033 mol) 1' gram of alpha trioxymethylene (0.033,mol)

0.2 gram of aluminum chloride (anhydrous) 50ml. benzene i The glycol, alpha trioxymethylene and the aluminum chloride weremixed with benzene. .The benzene was distilled. The water that distilled with the benzene was separated and the benzene was'returned to the reaction zone. When 0.6 ml. of water had been collected, the

' aluminum chloride was neutralized with potassium 'acetate. The solution was filtered and the benzene was removed under vacuum on the steam cone. The product was a thin liquid.

EXAMPLE The composition tested as described in Example X was prepared from the following components:

15 grams of Polyethylene Glycol 300 (0.05 mol) 20 grams of Polyglycol P-400 (0.05 mol) 3 grams of alpha trioxymethylene (0.10 mol) P 0.2 gram of ferric chloride x a 70 ml. of benzene The twoglycols, the alpha trioxy methylene and the The benzene was distilled and the water distilling with the benzene was separated and the; benzene returned to the reaction zone. When 1.8 ml. of water had been'collected,

10 the ferric chloride was destroyed with potassium acetate and the solution was filtered. The benzene was removed under vacuum at steam temperatures. The product was aviscous liquid. e l i In the foregoing examples the sofcalled Polyethylene Glycols followed by a number are the trade names for products made by Carbide and Carbon Chemicals Corporation having the general formula:

HOCH (CH' OCH CH OH CH3 HowrnaH'onHr and heptaoxypropylene glycol f CH3 [HO(CHz( JHO).-H]

The addition products employed for the purpose of the inventionmay also be prepared by reacting the aldehyde with a polyoxyalkylene glycol in which the oxyalkylene groups contain both oxyethylene. and 1,2-oxypropylene groups in the same molecule. Compounds of this type are described in U. S. Patent 2,425,845 and aresold under the trade name iUcon. Typical materials of this type which can be reacted with formaldehyde to produce addition products suitable for the practice of the present invention are Ucon 75 H 1400, Ucon 75 H 4900,"Ucon 75H 9150, andUcon 75 H 90,000 (Carbide and Carbon Chemicals Corporation); The preferred materials of this type are the polyoxyalkylene glycols in which the oxyalkylene groups consist of oxyethylene and 1,2-oxypropylene groups in an approximate weight'ratio within the range of 3:1- to 1:9.

The products-of the invention are preferably prepare by: reacting substantially equal mol quantities of the glycol and formaldehyde. If an excess of formaldehyde is used, part of it distils.

Where reference is made herein to molecular weights viscosity is defined as the limiting value of 'the specific viscosity divided by concentration, as concentration appreaches zero. 1 Specific viscosity is definedas follows:

where 1 and 1 are the viscosities of a solution of the polymerfata concentration, 0, and the viscosity of the solvent, respectively. Intrinsic viscosity is then expressed mathematically as Mag and is readily obtained by determining 1 at several values of concentration, c, plotting the experimental values of r asp/c for the various values of against 0; and extrapolatmg to c=0, whereby (1;) is obtained.

By the determination of intrinsic viscosity for a series of polymer mixtures, differing only in average polymer slze, it has been found that Where n in the formula is 2 and x is 23, the intrinsic viscosity in benzene should be greater than 0.135. When n is 3 (the larger oxyalkylene groups are 1,2-oxypropylene) and x is 7, the intrinsic viscosity in benzene should be greater than 0.040. When n is 'both 2 and 3 (e. g., the polymers contain oxyethylene groups and oxypropylene groups in a Weight ratio of approxlmately 1:1 and x had an average value of approximately 19) the intrinsic viscosity iiibenzene should be greater than 0.100.

The products hereinabove described may be liquid or low-melting wax-like solids, and in some cases may be rather hard solids which may be pulverized by grinding. They may be entirely soluble in cold water or only partially soluble. In the latter case, they are relatively easily dispersed in the feedwater by means of additional dispersing agents, as described above. All of the products exhibit substantial insolubility in hot water, the phenomenon of decreasing solubility in water with increasing temperature being characteristic of compounds of this class which contain multiple ether linkages and in which the ratio of ether linkages to carbon is sufliciently great to permit the weak hydrogen bonding effect of the ether oxygen to confer water solubility.

The amounts of an antifoam agent employed in inhibiting the foaming of water in a steam generator will depend upon several factors, among them the percent of solids in the foaming liquid, the nature of the solids, the alkalinity, temperature, and pressure, the type and degree of circulation in the steam generator, the rate of steam production, and the amount of foam suppression desired. It is therefore impossible to state any rigid rules for estimating the amount of an antifoam which needs to be used.- The amounts of the addition products of this. invention which are required are, however, extremely small. For many purposes, amounts of the order of 0.01 grain per gallon to 0.02 grain per gallon in the feedwater are sul'ficient, and under certain conditions'quantities as low as 0.001 grain per gallon in the feedwater have proved efiiective. In general, it can be said that quantities greater than 0.1 grain per gallon in the-feedwater would seldom be required.

In general where the addition product is incorporated with tannins, sodium lignin sulfonate and desulfonated lignins prior to adding it to the boiler feedwater, the quantity of the' addition product is within the range of 0.5% to 12% by weight of the total composition and the total quantity of tannins, sodium lignin sulfonate and/or desulfonated lignins is within the range of about 50% to about 97% by weight of the composition.

The practice of the invention is applicable to the inhibition of foaming in steam generation over a relatively wide pressure and temperature range. In locomotive boilers, steam is generally generated at pressures around 250 pounds per square inch and the corresponding temperatures. Excellent results have been obtainedwith the practice of the invention at pressureswithin the range of 100 to 300 pounds per square inchv and the corresponding temperatures. The invention can also be used, however, in connection with the generation of steam at much higher pressures and the corresponding temperatures, as, for example, in stationary boilers operating at pressures as high as 1000 to 1500 pounds per square inch. The compositions employed in accordance with the invention are effective not only in inhibiting foaming but also in conditioning and improving the quality of the steam. For this purpose, they may be used in even smaller amounts than the amounts required other organic water treating chemicals of the tannin and lignin types in treating many water supplies as will be seen from the following. On waters high in magnesium salts in which the magnesium in the boiler will generally be in the form of magnesium hydroxide, it is desirable that sufficient of hydroxylated organic material such as tannins, tannic acid, gallic acid, pyrogallol, catechol, phloroglucinol, etc., be added along with the addition products. These hydroxylated organic compounds have the ability of nullifying the bad elfects of the magnesium hydroxide. Magnesium hydroxide appears to partially selectively adsorb the antifoam material and so take it out of the boiler water so that the full antifoam action cannot be exerted by the antifoam compositions when in this adsorbed state. However, when an organicmaterial such as a tannin is added, magnesium hydroxide appears to lose its ability to interfere with-the antifoam action. Inasmuch as most boiler feedwaters encountered will have varying amounts of magnesium salts present, it is desirable that such hydroxylated organic compounds be mixed with the antifoam ingredients prior to addition to the boiler feedwater.

It will be understood that the tannins, sodium-lignin sulfonate and/or desulfonated lignins are not necessarily incorporated with the antifoam composition prior to the addition of the latter to the feedwater. Where it is desirable to use tannins, sodium lignin sulfonate and/or desulfonated lignins,- these substances may also be added directly to the boiler Water. The following table illustrates the quantity of the tannins, sodium lignin sulfonate and/or desulfonated lignins which can be employed satisfactorily to nullify the action of the magnesium salts on the addition products.

Table I Magnesium, Grains Per Gallon in Boiler Water (Expressed as 0&(303) The advantage is evident in preparing and using the pulverized or briquetted compositions hereinabove described containing both the antifoam and the polyhydroxylated organic material of the tannin or ligninderivative type.

The present application is a continuation-in-part of my copending application Serial No. 224,250, filed May 2, 1951, now abandoned, which in turn 'was' a continuation-in-part of my application Serial No. 123,103, filed October 22, 1949, now abandoned.

The invention is hereby claimed as follows:

1. A method of generating steam from a boiler water having a tendency to foam on boiling which comprises dispersing insaid Water a quantity of a polyoxyalkylene diol having a plurality of interconnected oxyalkylene groups, each containing 2 to 10 carbon atoms, interlinked with a suflicient number of groups to produce a diol having an average molecule weight within the range of 1000 to 11,500 and having hydroxyl groups attached to terminal carbon atoms,'said diol being substantially insoluble in said boiler water at the temperature of steam generation, the quantity of said diol being etfective to inhibit the tendency of said water to foam on boiling, and heating the resultant aqueous dispersion to the boiling point.

l 13 2. A method of generating steam from a boiler water having a tendency to foam on boiling which comprises dispersing in said water a quantity. of a compound having the following general formula wherein n is an integer from 2 to 3, x and y are integers, the average molecular weight is within the range from 1000 to 11,500 and the compound is substantially insoluble in said boiler water at the temperature of steam generation, the quantity of said compound being eifective to inhibit the tendency of said water to foam on boiling, and heating the resultant dispersion to the boiling point.

3. A method of generating steam from a boiler water having a tendency to foam on boiling which comprises dispersing in said water a quantity of anaddition product of alpha-trioxymethylene and a polyoxyalkylene glycol having two terminal hydroxyl groups spaced by at least 4 carbon atoms and in which the oxyalkylene groups contain 2 to 5 carbon atoms, said addition product having a molecular weight within the range of 1000 to 11,500 and being substantially insoluble in said boiler water at the temperature of steam generation, the quantity of said addition product being effective to inhibit the tendency of said water to foam on boiling, and heating the resultant aqueous dispersion to the boiling point.

4. A method of generating steam from a boiler water having a tendency to foam on boiling which comprises dispersing in said water a quantity of an addition product of alpha-trioxymethylene, a polyoxyethylene glycol having two terminal hydroxyl groups spaced by at least 4 carbon atoms and having a molecular weight of approximately 300 and a polyoxypropylene glycol having a molecular weight of approximately 400 reacted in a molar ratio of approximately 2:1:1 and being substantially insoluble in said boiler water at the temperature of steam generation, the quantity of said addition product being effective to inhibit the tendency of said water to foam on boiling, and heating the resultant aqueous dispersion to the boiling point. 7

5. A method of generating steam from a boiler Water I having a tendency to foam on boiling which comprises dispersing in said water a quantity of an addition product of alpha-trioxymethylene and polyoxypropylene glycol having two terminal hydroxyl groups spaced by at least 4 carbon atoms and having a molecular weight of at least 400 reacted in approximately equimolar proportions and being substantially insoluble in said boiler water at the temperature of steam generation, the quantity of said addition product being effective to inhibit the tendency of said water to foam on boiling, and heating the resultant aqueous dispersion to the boiling point.

6. A boiler water comprising a water containing magnesium compounds and an amount of total dissolved solids tending to produce foaming and priming when heated to the boiling point, a quantity of a foam inhibiting compound corresponding to from 0.001 grain to 0.1 grain of said compound per gallon of said water, said compound being an addition product of alphatrioxymethylene and a polyoxyalkylene glycol having two terminal hydroxyl groups separated by at least 4 carbon atoms and in which the oxyalkylene groups contain 2 to 5 carbon atoms, said addition product having a molecular weight within the range of 1000 to 11,500 and being substantially insoluble in said boiler water at the temperature of steam generation, and a quantity of a hydroxylated organic compound dispersed in said water from the group consisting of tannins, sodium lignin sulfonate and desulfonated lignins, said quantity being effective to nullify the action of the magnesium compounds on said addition product.

7. A boiler water comprising a water containing mag; nesium compounds and an amount of total dissolved solids tending to produce foaming and priming when heated to the boiling point, a quantity of a foam inhibiting compound corresponding to from 0.001 grain to 0.1'.

grain of said compound per gallon of said water, said compound being an addition product of. alpha-.trioxymethylene and polyoxyethylene glycol having two terminal hydroxyl groups separated by at least 4 carbon atoms and having a molecular weight of approximately 1000 reacted in a molar ratio of approximately 141 and being substantially insoluble in said boiler water at the temperature of steam generation, and a quantity of a hydroxylated organic compound dispersed in said water from the group consisting of tannins, sodiumlignin sulfonate and desulfonated lignins, said quantity being effective to nullify the action of the magnesium compounds on said addition product.

8. A boiler water comprising a Water containing magnesium compounds and an amount of total dissolved solids tending to produce foaming and priming when heated to the boiling point, a quantity of a foam inhibiting compound corresponding to from 0.001 grain to 0.1 grain of said compound per gallon of said water, said compound being an addition product of alpha trioxymethylene and polyoxypropylene glycol having two terminal hydroxyl groups separated by at least 4 carbon atoms and having a molecular weight of at least 400 reacted in approximately equimolar proportions and being substantially insoluble in said boiler water at the temperature of steam generation, and a quantity of a hydroxylated organic compound dispersed in said water from the group consisting of tannins, sodium lignin sulfonate and desulfonated lignins, said quantity being effective to nullify the action of the magnesium compounds on said addition product.

9. A boiler water comprising a water containing magnesium compounds and an amount of total dissolved solids tending to produce foaming and priming when heated to the boiling point, a quantity of a foam inhibiting compound corresponding to from 0.001 grain to 0.1 grain of said compound per gallon of said water, said compound being an addition product of alpha-trioxymethylene, a polyoxyethylene glycol having a molecular weight of approximately 300 and a polyoxypropylene glycol ahving a molecular weight of approximately 400 reacted in a molar ratio of approximately 2:1:1, said glycols having two terminal hydroxyl groups separated by at least 4 carbon atoms and said compound being substantially insoluble in said boiler water at the temperature of steam generation, and a quantity of a hydroxylated organic compound dispersed in said water from the group consisting of tannins, sodium lignin sulfonate and desulfonated lignins, said quantity being efiective to nullify the action of the magnesium compounds on said addition product.

10. An antifoam composition for minimizing the production of foam in the generation of steam from water containing magnesium compounds which comprises essentially 0.5% to 12% by weight of an addition product of alpha-trioxymethylene with a polyoxyalkylene glycol having two terminal hydroxyl groups spaced by at least 4 carbon atoms and in which the oxyalkylene groups contain 2 to 5 carbon atoms, said addition product having a molecular weight of at least 1000 and being substantially insoluble in boiler water at steam generating temperatures, and approximately 50% to 97% by weight of a substance from the group consisting of tannins, sodium lignin sulfonate and desulfonated lignins.

11. An antifoam composition for minimizing the production of foam in the generation of steam from watercoutaining magnesium compounds which comprises essentially 0.5 to 12% by weight of a compound having the following general formula wherein nis an integer from 2 to 3, x and y are integers, the average molecular weight is within the range from 1000 to 11,500 and the compound is substantially insoluble in boiler water at steam generating temperatures, and ap- 15 proximately 50% to 97% by Weight of a substance from the group consisting of tannins, sodium lignin sulfonate and desulfonated lignins.

12. An antifoam composition for minimizing the production of foam in the generation of steam from Water containing magnesium compounds which comprises essentially 0.5% to 12% by weight of a polyoxyalkylene diol having a plurality of interconnected oxyalkylene groups, each containing 2 to 10 carbon atoms, interlinked with a sufficient number of oxymethylene groups to produce a diol having an average molecular Weight within the range of 1000 to 11,500 and having hydroxyl groups attached to terminal 155 carbon atoms, said diol being substantially insoluble in boiler water at steam generating temperatures, and approximately 50% to 97% by Weight of a substance from the group consisting of tannins, sodium lignin sulfonate and desulfonated lignins.

References Cited in the file of this patent UNITED STATES PATENTS Gunderson Mar. 3, 1953 

1. A METHOD OF GENERATING STREAM FROM A BOILER WATER HAVING A TENDENCY TO FOAM ON BOILING WHICH COMPRISES DISPERSING IN SAID WATER A QUANTITY OF A POLYOXYALKYLENE DIOL HAVING A PLURALITY OF INTERCONNECTED OXYALKYLENE GROUPS, EACH CONTAINING 2 TO 10 CARBON ATOMS, INTERLINKED WITH A SUFFICIENT NUMBER OF 